A. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a good image quality and wide viewing angle liquid crystal display device.
B. Description of the Prior Art
Conventional twisted nematic liquid crystal display devices (TN LCD) have a contrast angular dependence problem, i.e., the transmittance in each gray level depends on the viewing angle. In particular, this contrast angular dependence is very strong in the up and down directions. The angular dependence is caused by the phase difference according to the viewing angle which generates the birefrigence of the liquid crystal molecule.
To solve this angular dependence problem, a multi-domain LCD such as a two-domain TN LCD (TDTN LCD) and a domain divided TN LCD (DDTN LCD) have been introduced. In the TDTN LCD, each pixel has two director configuration domains, where the two pretilted directions are in opposing directions. Applying a gray level voltage to this LCD, the LC directors in the two domains are listed in opposite directions. These configurations average me up and down direction transmittance. In the DDTN LCD, materials having different pretilt angles, such as organic or inorganic materials, are alternately exposed in the each pixel. By the aligning process, each exposed area, i.e., each domain has a pretilt angle different from that of the neighboring domain.
FIG. 1A is a plan view of a conventional multi-domain LCD and FIG. 1B is a sectional view taken on line A-A' of FIG. 1A. As shown in these figures, a plurality of gate bus line 7 and data bus lines 9 cross each other, thereby defining the pixel region. At the cross of the gate bus lines 7 and the data bus lines 9, a plurality of thin film transistors of which gate electrodes 5 and source/drain electrodes 3 are respectively connected to the gate bus lines 7 and the data bus lines 9, are formed. A part of the gate bus lines 7 is used as an electrode for the storage capacitor. In this type, the metal layers 13 are formed on the gate bus lines 7 to stabilize voltage to the liquid crystal cell. In each pixel region, first and second alignment layers 17 and 18 are coated and then aligning-processed to divide the 4-domains having different alignment directions, as shown in FIG. 1B.
In a pixel having a plurality of domains, since the LC directors in neighboring domains are directed in the opposite or different directions, there are discrete planes of the alignment in the boundary region between the neighboring domains, as shown in FIG. 1B. Thus, when transmitting light through liquid crystal layer 25, the light leaks through the boundary region (line X-X' of FIG. 1B) between the domains. As a result, the disclination is generated in these regions.
To prevent the leakage of the light, black matrix 11 must be formed in the boundary region to shield the light entering this region, as shown in FIGS. 1A and 1B, but this black matrix 11 causes an aperture ratio problem. In addition, since the metal layer 13 for the storage capacitor covers gate bus lines 7 as well as a part of the pixel region, the aperture ratio characteristic is further deteriorated.